The present invention relates to an etching system and an etching method; and, more particularly, the invention relates to an etching system and an etching method that can suppress the influence of disturbances.
In an etching system using a plasma, for example, an etching gas is introduced into a vacuum process chamber, and a plasma discharge is produced under a reduced pressure; whereby, radicals or ions generated in the plasma are led to the surface of a wafer, which serves as the workpiece to be processed, and a reaction is caused at the wafer surface, thereby performing etching of the wafer surface. The etching system for performing such a processing (dry processing) is operated so as to carry out etching based on preset production conditions (gas flow rate, gas pressure, electric power supplied, etching time, etc.), hereinafter called a “recipe”.
The recipe is generally maintained constant during a production step (an etching step for a single film to be etched) of a specified process, such as for the production of semiconductor devices, excluding a process for production of a photomask or the like, in which, for example, one process is divided into several steps and production conditions are modified on the basis of each step.
However, even if a fixed etching using a fixed recipe is carried out, various disturbances, such as those caused by a secular change in the system, make it difficult to constantly obtain a fixed performance. As a method of suppressing such disturbances, for example, Japanese Patent Application No. 2001-198830 discloses a technique in which the processed results are monitored and information is fed back to the recipe based on the monitored results.
In the case of monitoring the results of processing a specimen, such as a semiconductor wafer, and feeding back the monitored results to the recipe, the elements constituting the recipe include a number of parameters, such as gas flow rate, pressure, electric power supplied, and etching time. In order to specify an optimum parameter for control from among these parameters and build up a control model by use of the specified parameter, it is necessary to perform a number of experiments and simulations, which involve an enormous effort and a substantial amount of time.
In addition, even if the optimum control model is built up, unexpected side effects may be generated. For example, in a gate etching step for forming a gate electrode of an FET (Field Effect Transistor), etching which does not impair a thin gate insulation film, that is present beneath the film to be etched, is required for avoiding undesirable influences on the device performance. However, in the case where the characteristics of the system are varied in the direction of worsening the selectivity ratio between the film to be etched and the gate insulation film, as a result of the feedback of the monitored results to the recipe, the gate insulation film is also processed, with the result that the gate insulation film may be damaged.
That is, even where an attempt is made to restrain various disturbances by feedback control, realization of this objective in an actual production process requires an enormous effort and significant time, and, still, there is a fear of unexpected side effects.